In a rack-and-pinion type steering apparatus, a rack shaft having rack teeth meshing with the teeth of a pinion is movably supported through a bush bearing by a gear box serving as a housing. As bush bearings, synthetic resin-made bush bearings have been variously proposed, and such a synthetic resin-made bush bearing is generally adapted to movably support the rack shaft with an interference (refer to Patent Document 1).
In the synthetic resin-made bush bearing, if a large interference is provided for the rack shaft to be supported, the rack shaft can be supported firmly in an radial direction thereof with predetermined rigidity. However, since the rack shaft is tightened tightly, frictional resistance against sliding in the axial direction becomes large, so that it becomes impossible to support the rack shaft with a satisfactory moving characteristic. On the other hand, if a small interference is provided for the rack shaft to be supported, a satisfactory axially moving characteristic having low frictional resistance against sliding on the rack shaft can be expected. However, a large axial offset of the rack shaft and a gap between the bush bearing and the rack shaft, among others, are likely to occur, so that the rigid support in the radial direction disadvantageously declines.
To overcome the above-described aspects, in Patent Document 2, a bush bearing is proposed which is comprised of: a synthetic resin-made bush having at least one circumferential groove in an outer peripheral surface thereof; and an endless annular elastic member which is fitted in the circumferential groove of the bush, wherein the bush has a pair of inside inner peripheral surfaces which are disposed axially symmetrically; a pair of slits which are each disposed with one of the inside inner peripheral surfaces located therebetween in a circumferential direction, and allow that inside inner peripheral surface to be movable in a radially inward/outward direction; another pair of slits which are each disposed with the other one of the inside inner peripheral surfaces located therebetween in the circumferential direction, and allow that inside inner peripheral surface to be movable in the radially inward/outward direction; and at least one pair of outside inner peripheral surfaces disposed on an outer side than the pair of inside inner peripheral surfaces in a radial direction, wherein each of the outside inner peripheral surfaces is adapted to form a gap with a corresponding one of outer peripheral surfaces on a rack teeth side and an opposite side to the rack teeth side of a rack shaft which is inserted and fitted in a through hole defined by the pair of inside inner peripheral surfaces and the pair of outside inner peripheral surfaces, and wherein each of the inside inner peripheral surfaces at least at the portion is adapted to slidably come into contact with a corresponding outer peripheral surface of the rack shaft, excluding outer peripheral surfaces on the rack teeth side and the opposite side to the rack teeth side of the rack shaft.